The 2013 Mercedes-Benz SL550 is the newest player in the premium sport convertible segment, and with a base price of over $100,000 and an all-new 429-horsepower twin-turbo V8, it ticks those boxes handily.
But it's not alone in the segment.

BMW also has a twin-turbo V8-powered luxury sport convertible in the form of the 2012 BMW 650i. It has more seats and costs less, but the 4.4-liter V8 in the BMW only makes 400 horsepower and 450 pound-feet of torque. It's also backed by an eight-speed automatic, while the SL makes do with only seven forward gears.

With more power and less weight, the 2013 SL550 is expected to walk the BMW in performance testing, but is it enough to justify the price and lack of rear seats? Check the numbers after the jump and make the decision for yourself.

Acceleration: "Eco" mode disabled (so the engine is running), the default traction control is exceptionally good -- allowing a teeny bit of wheelspin. I barely "beat" it with my own, non-wheelspin launch. There's obviously enough torque to light the tires, but this only makes it slower. Power feels linear despite turbocharging. This engine reminds me very much of the "old" AMG 6.2 with its pull all the way up to redline. Upshifts are blazingly fast and smooth, as are matched-rev downshifts. Wow. (Still auto-upshifts in Manual mode).

Braking: Short and consistent distances. Every stop was absolutely fade-free (feel + distance) and dead straight, with no drama whatsoever. Felt like it would do the same stop all day long. ABC kept the car flat.
Handling:

Skid pad: With ESC off, the SL feels quite "free," requiring a lot of attention through throttle and steering to maintain a consistent arc. Steering, however, doesn't offer much feel or building effort, but is friction-free and precise. With ESC On, the throttle is subtly, almost imperceptibly manipulated and possibly brakes as well. I was "less busy" and the results were slightly better.

Slalom: Good initial steering response, but then by the second cone, the SL feels a half step behind with its ABC, and ESC is not truly off. Also, the unintuitive lack of suspension load and resulting body roll is further disconcerting. Best run was to cause the least amount of upset with the minimum amount of steering input, instead favoring the throttle to affect yaw. With ESC on, the differences were so slight (and perhaps non-existent) and boiled down to heated tires(?) or a reluctant throttle at the exit cone.

Acceleration The default mode (Normal/Drive) hesitates slightly from a dead stop. Each successive mode makes the car slightly quicker (Sport, Sport+ and DS and manual). Once underway, the power comes quickly (perhaps due to gearing) and seems to carry all the way to the 7K(?!) redline. I "beat" traction control with a two-footed non-wheelspin launch with Trac off. Upshifts are both fast and smooth, as are matched-rev downshifts. (Still auto-upshifts in Manual mode).

Slalom: With ESC off (in Sport), slightly delayed initial steering response, and the car grows increasingly tail-happy, especially off-throttle. Going in with maintenance throttle or trying to catch each slide, I always felt like I was a step behind. It requires a slow-in/fast-out technique to maintain rear bias and grip throughout. The active suspension is disconcerting and doesn't offer expected seat-of-the-pants feedback. With ESC on (in Sport+), I could be less concerned with the loose rear end and focus on car placement. Also, it was simple to whack the throttle to the mat and let traction control take care of things.

Skid pad: With ESC off (in Sport), the 650 feels well-balanced between under/oversteer. It's easy to hold to the line. Steering, however, is rather numb and the throttle response is a little lazy to use as yaw controller. With ESC on (in Sport+), I couldn't detect any intrusion at all, hence the near-identical numbers.

The merc is nice, but it's not an apples and apples comparison by any means. The merc is a 2 seater, more powerful, weighs over 400lb less, and costs over 20k more. It costs more than the new M6. Mercedes doesn't really have a direct competitor to the 650i.

The merc is nice, but it's not an apples and apples comparison by any means. The merc is a 2 seater, more powerful, weighs over 400lb less, and costs over 20k more. It costs more than the new M6. Mercedes doesn't really have a direct competitor to the 650i.

Technically they're not direct rivals, but people will cross shop both cars, so it's a valid comparison test.

Technically they're not direct rivals, but people will cross shop both cars, so it's a valid comparison test.

I totally agree that some may cross shop in terms of higher end sport cabs, but I think many would be cross shopping an M6 with the SL as well. Merc has certainly stepped up their game and I look forward to test driving both, but I personally can't imagine choosing the SL over the M6 cab. They differ in price by about 8k usd.

Wow, love the vid. I can't really choose as I do like them both. I like the 650 but I also think that the SL550's also a great car. Parts for Mercedes don't really have a large price margin difference than from a bimmer, so that also weighs on why i can't really chose. I guess I'd go with the 650